1. Field of the Invention
The invention relates to data processing systems and, more particularly, to data processing systems employing multiple buses.
2. Discussion of the Related Art
In computers and data processing systems, a bus is commonly employed to interconnect the various elements of the system. For example, a central processing unit is typically connected to memory components, input/output (I/O) devices, etc., via a bus capable of carrying the signals associated with the operation of each element. These signals include, for example, data signals, clock signals, and control signals. The bus must be capable of carrying such signals to all components coupled to the bus so that the desired operation can be carried out by the computer system.
As computer systems achieve increasingly higher levels of performance, it is sometimes desirable to provide more than one bus in the computer system. For example, it may be desirable to provide a high speed main system bus which interconnects processors and high speed memory components, and to provide a separate bus which interconnects I/O devices such as disk drives and tape drives to an I/O controller.
Initially, manufacturers of computer systems provided proprietary buses with which to interconnect components of the system. There is now an increasing trend toward the use of standardized buses, in which specifications of the bus are published for use by all manufacturers. Many manufacturers can then supply components specifically for use with the standard bus.
Multiple standard buses are now available, each having a different set of characteristics. However, there is an increasing need to provide the capability to assemble computer systems employing components connected to various types of standard buses. Methods and apparatus for providing such interconnections are known in the art. Known interconnection systems employ serial lines, ribbon cable, and fiber optics. For example, methods and apparatus for interconnecting computer buses using an interconnection known as the IBUS are described in U.S. Pat. No. 4,858,234 issued Aug. 15, 1989 to David W. Hartwell et al., and assigned to the assignee of the present invention.
As a result of such trends, the importance of various features of an interconnection system is becoming apparent. For example, it is desirable for an interconnection system to provide high data transfer rates between buses, such that functionality on high performance buses is not compromised due to waiting time caused by an inefficient bus interconnection system. It is further desirable to provide methods and apparatus for interconnecting information buses of different sizes and to provide interconnection between different cabinets, without requiring a backplane connection between buses. Intercabinet connectivity gives rise to the need for high noise immunity and, correspondingly, low noise emissions. It is further desirable to provide methods and apparatus for interconnecting buses which utilize the minimum number of interconnection lines.
With the increasing number of standardized buses, it is important for a manufacturer to enable interconnectivity of the manufacturer's products with as wide a variety of standard bus systems as possible. Implementation of custom interconnection methods and apparatus for each bus pair gives rise to high design and manufacturing cost. It is therefore desirable to provide apparatus and methods for interconnecting information buses which are extremely flexible, and employ a large number of common components to permit multiple interconnection applications with a minimum of cost.
None of the known methods and apparatus for interconnecting information buses fully meet the requirements noted above.